Pattern matching function declarations in Python

All those who have tried to write a rules-based program know that there are, at least, two differences between "regular" programming and rules-based programming. The first is that you have no direct control over the flow of execution and the second is that, instead of specifying input parameters, you specify patterns that should be matched for a certain "function" (or rule) to be invoked.

The bit about giving up control is quite difficult for most programmers (at least the ones I know) and it doesn't translate well to other types of programming anyway. But it would be interesting to try and add pattern matching functions to a language such as Python and see whether it could be useful (or at least fun to experiment with).

It's not a new idea. The first language to support pattern matching this way was Snobol (version 4 I think) which was introduced in the late 60s/early 70s. Both Haskell and Erlang has it and there are a bunch of others as well, Qi and Prolog to mention a few.

I'm thinking about something along the lines of:

>>> from patternmatching import *
>>> @patternmatched
... def fac(n = 0):
...   return 1
...
>>> @patternmatched
... def fac(n = int):
...   return n* fac(n = n-1)
...
>>> fac(5)
120
>>>

The idea is that the first function would handle any calls to the fac function where the parameter n is 0 and the second function would handle any calls where the parameter n is an int (but not 0). And, yes. I've got the above working already. The tricky bits are providing more elaborate forms of pattern matching with the available syntax.

I'll be back shortly with some code...